[Elecraft] KPA500 Minimum Drive?

[Fred Jensen]

Hmmm ... I guess first question is, what's the problem?  25 W to 20W is 
slightly less than 1 dB, 0.16 S-unit.  Just run barefoot?

The LED Power display on the KPA500 is digital.  It "measures the 
power," and puts it into one of a number of bins.  If something is in 
the bin, it lights the LED.  If the measured power isn't high enough for 
the lowest bin, all the bins are empty, no LED's light up, although 
there is still RF being made.

Measuring power with simple instruments is hard ... well, sort of 
impossible.  You can measure the voltage, but then you need to know the 
impedance, a complex number, not easily measured with a DVM.  You can 
measure the current -- same problem.  KPA500 is designed to emit 500W 
with 25-30W input.  I think you're pushing the envelope here and nothing 
is wrong.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the Cal QSO Party 1-2 Oct 2016
- www.cqp.org

On 6/15/2016 4:54 PM, James Bennett wrote:
> I share my KPA500 with a K3 and a KX3. When I want to operate JT65 or
> JT9 I normally run about 25 watts out, using the KX3 to drive the
> amp. With the KX3 set to 1.8 watts out, the amp gives me 25; with 2.2
> watts from the KX3, I get 30 watts out from the amp.
>
> But, what if I want to run 20 watts? Or 15? When I back the KX3 power
> level below 1.8, the KPA500 shows zero on the LED power display. Does
> this mean it is no longer amplifying, or is it actually amplifying
> but not enough for the circuitry to determine how much?
>
> Jim Bennett / W6JHB Folsom, CA